(a) Field of the Invention
The present invention relates to a portable detector device for detecting partial electrical discharge in live voltage distribution cables and/or equipment located above or below ground (such as in manholes).
(b) Description of Prior Art
Electrical utilities share a keen interest in technological advances that promise better reliability and greater safety of their power transmission and distribution systems. They invest heavily in the evaluation of system components, control and communication equipment, installation and non-destructive measurement techniques in an aim to minimize power outages and the duration of any unavoidable system down time. Service continuity is often difficult to maintain due to existing conditions of cables and joints without jeopardizing the safety of operating personnel required to maintain and repair the distribution lines and equipment.
Electrical utilities are always striving to improve the safety of their personnel working in manholes or above ground on the utilities' extensive distribution network. Therefore, there is a need to provide a simple portable tool for checking the state of cables and joints in manholes or above ground, and that would ensure greater safety to the user and which could evaluate partial discharge levels in cables and joints in normal system operating conditions. Partial discharge measurement represents the most informative non-destructive test of the quality of extruded solid dielectrics, since the presence of such discharges at operating voltage, gives a positive indication of serious problems in the near future.
However, partial discharges are very difficult to measure owing to the need to eliminate extrenuous electromagnetic interference while maintaining the supply of high cable charging current. Balanced bridge circuity using low frequency (0.001 hz) test source is one solution, although it is not as easy to use as a general go or no-go test. There is, therefore, a need to provide a detector device capable of detecting non-electrical signals, in decibals, microvolts, etc. that could be related to partial discharges measured by standard techniques (in microcoulombs).